As a noun meff
is an objectionable, an unkempt person or a tramp.
As an adverb deff is
alternative form of definitely.
meff
English
Noun
(
en noun)
(Liverpool, pejorative) An objectionable, an unkempt person or a tramp.
References
* A Dictionary of Slang and colloquialisms of the UK
* Merseytalk - see under section M